As disclosed in U.S. Pat. No. 8,058,486, the compound 1,1,2,3-tetrachloro-propene (HCC-1230xa) is an important precursor that can be used for the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf), which is a low GWP molecule that can be used as an effective refrigerant, fire extinguishing agent, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric agent, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid, to name but a few.
HCC-1230xa can be made in a known four-step process, as follows:CCl4+CH2═CH2→CCl3—CH2—CH2Cl  (1)CCl3—CH2—CH2Cl→CCl2═CH—CH2Cl+HCl  (2)CCl2═CH—CH2Cl+Cl2→CCl3—CHCl—CH2Cl  (3)andCCl3—CHCl—CH2Cl→CCl2═CCl—CH2Cl+HCl  (4)
As shown above, in Step 3 of this four-step process, 1,1,3-trichloropropene (HCC-1240za) from Step 2 is used as the starting material, where HCC-1240za is chlorinated by Cl2 to form the intermediate product 1,1,1,2,3-pentachloropropane (HCC-240db) under specific reaction conditions:CCl2═CH—CH2Cl (HCC-1240za)+Cl2→CCl3—CHCl—CH2Cl (HCC-240db)Then, HCC-240db is dehydrochlorinated by a catalyst (such as FeCl3 or equivalents) to form HCC-1230xa and HCl in Step 4:CCl3—CHCl—CH2Cl (HCC-240db)→CCl2═CCl—CH2Cl (HCC-1230xa)+HCl
In normal practice, the crude product from the third step is used directly as the starting material for the fourth step reaction without further purification.
In this invention, it has been found that the crude HCC-240db containing HCC-1240za from the Step 3 reaction and/or HCC-250fb (1,1,1,3-tetrachloropropane) carried over from the Step 2 distillation, inhibited the conversion of HCC-240db to HCC-1230xa in the Step 4 reaction.